My Tare K'uhd ("Deep Waters") campaign setting turns into some twenty-six pages in my notebook. But I started getting into prehistoric history as well as life aquatic. This lead to this map on the eighth page of these scribblings.
An advanced, well bronze-age, human culture was exploring these strange waters. These humans were viewed like martians from another planet by the locals. They were based off south Asian Harappan culture. I was attending lectures on India at a local library at the time. I drew up this map for my academic notes.